This invention relates to product forms of N-halohydantoin compounds, and more particularly to densification of N-halohydantoin forms. Still more particularly, this invention relates to the densification of dry N,N'-dihalohydantoin particulate solids mixed with chemical additives into tablets that withstand the stresses of automatic packaging, conveying handling, shipping, storage and use equipment.
N-halohydantoin compounds are highly efficient halogen donors for effecting various organic syntheses. In water, such compounds provide a low concentration of active halogen and are thus useful as bacteriocides in water treatment processes. Particularly effective halogen sources are N,N'-dihalohydantoin compounds such as 1-bromo-3-chloro-5,5-dimethylhydantoin, 3-bromo-1-chloro-5,5-dimethylhydamtoin, 1,3-dibromo-5,5-dimethylhydantoin and 1,3-dichloro-5,5-dimethylhydantoin.
N-halohydantoin compounds are ordinarily produced as particulate solids. However, for certain uses, it is desired to compact, agglomerate, extrude or otherwise densify particulate N,N'-dihalohydantoin compounds into forms such as tablets or briquettes. For such purposes, it is necessary to utilize a formulation which, when formed under mechanical pressure into a predetermined shape, is strong enough to withstand the shocks, stresses and pressures resulting from automated packaging, conveying, handling, shipping, storage and use equipment. Conventionally, it is necessary for tablets formed from particulate N,N'-dihalohydantoin compounds to be oven dried or "cured" to possess sufficient strength or "hardness" to withstand subsequent handling and packaging operations. Oven-drying is undesirable, however, because it requires an extra processing step, uses energy and requires further delays for cooling.
Other problems exist in the conventional methods of compressing N-halohydantoin compounds. The essentially unavoidable presence of some water, even at concentrations of only one-half to five percent, results in corrosion of the compaction equipment by the acidity produced by hydrolysis of the N-halohydantoin in the tablet. Another disadvantage of the conventional methods is that the acidity produced by hydrolysis of N,N'-dihalohydantoin compounds within the densified products reduces alkalinity in treated waters.
Various chemical additives have been introduced to N,N'-dihalohydantoin for various purposes. U.S. Pat. No. 3,412,021 (Paterson) discloses a method (and product formed thereby) involving the mixing of 1-bromo-3-chloro-5,5-dimethylhydantoin with various additives in the presence of copious water. In column 4, lines 67-69, it is noted that polymers added as binders are added as solutions, including aqueous solutions. These binders are added to enable the forming of sticks or rods and to reduce the disintegration rate of N,N'-dihalohydantoin in water. Further, in each example in the patent, sufficient water is added to form a paste consisting of at least 25% water.
Since excessive water in the product will render the chemical additive inactive pertaining to its curing properties, the method of Paterson does not yield acceptable tablets of N-halohydantoin compounds. Nor does the method of Paterson produce such tablets of increased hardness unless subjected to oven drying.
Paterson also does not disclose compressing or densifying the mixture. The method of Paterson consists of wet-forming (again, copious water is required) the halogenated compound by molding or extrusion. The method disclosed in Paterson improves the strength of the particulate so as to enable the mixture to be formed into sticks. After the mixture is extruded and dried, interstices previously occupied by water constitute voids within the crystalline structure. While the binders added in Paterson allow the formation of rods, the density of the mixture is actually decreased. The rods are therefore fragile and do not withstand stresses from the packaging equipment. Tablets cannot be formed by compression when the water content approaches that suggested by Paterson. At such water concentrations, excess alkalinity in the chemical additive reacts with acidity produced by hydrolysis of N-halohydantoin compounds, causing the chemical additive to become inactive and hardening is not achieved. Therefore, even upon the advent of Paterson, there was still a need for a method to create densified N-halohydantoin which can withstand the stresses of the automated handling equipment.
Moreover, many disadvantages have arisen from the use of chemical additives. For example, the chemical additives may react with the N,N'-halohydantoin compound or otherwise interfere with the desired uses of the N,N'-halohydantoin compounds, such as by reducing the dissolution rates of the compounds.